Finnish-Swedish composer, conductor and piano accompanist, born August 14, 1869 in Viborg, Finland, died June 23, 1958 in Stockholm, Sweden.

He studied with Ferruccio Busoni in Helsinki and with Jules Massenet in Paris. Both Järnefelt and Busoni enjoyed a close relationship with Jean Sibelius, who was married to Järnefelt's sister Aino. From 1905 Järnefelt had a long career as conductor at the Royal Swedish Opera in Stockholm, beginning as repetiteur from 1905 to 1911 (he became a Swedish citizen in 1909); conductor 1911-1923 and chief conductor 1923–1933.

Between 1932 and 1936 Järnefelt was the artistic director and conductor of the Finnish National Opera. He presented, among others, Siegfried and Götterdämmerung from Wagner's Ring cycle, and Parsifal. He was the principal conductor of the Helsinki Philharmonic Orchestra 1942–1943, and also returned to the Royal Swedish Opera as chief conductor from 1938 to 1946.